【作者】 任继文；

【导师】 张鸿海； 刘胜；

【作者基本信息】 华中科技大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 目前,平板式ZrO₂汽车氧传感器由于尺寸小,响应快,能耗低,易集成,在恶劣环境下工作稳定等优点成为汽车尾气控制的主流氧传感器,本文围绕氧传感器的制备工艺流程所涉及的粉体制备、成型烧结、器件制备与测试、材料表征等技术,展开以下相关技术基础研究,主要内容如下:采用适合于工业生产的化学共沉淀方法制备了掺杂8mol% Y₂O₃全稳定氧化锆超细粉（8YSZ）,应用激光粒度分析仪、热重-差热分析（TG-DTG）、X射线衍射分析（XRD）、扫描电镜（SEM）等手段对粉体进行了表征,研究了粉体制备过程中团聚形成的机理,讨论了溶液浓度、pH值、沉淀方式、沉淀温度、洗涤方式、表面改性和煅烧温度等工艺参数对粉体粒度分布的影响,并总结出各工艺参数的合理值。基于球形气孔模型建立了烧结中期和后期的显微结构模型,推导出了固相烧结中期和后期的致密化方程。选择粉体粒度与团聚程度不同的8YSZ粉体,对其进行干压成型、无压烧结实验。结合致密化方程,改变烧结工艺参数,测试烧结瓷体微观形貌、密度及收缩率等性能指标,阐述了烧结温度、粉体粒度、素坯密度和团聚等因素对瓷体致密度的影响。利用晶粒生长动力学,结合实验结果研究了陶瓷单相系统晶粒正常生长的规律,以及烧结温度、掺杂第二相Al₂O₃和素坯中气孔尺寸分布对8YSZ瓷体晶粒尺寸的影响,得到了获得致密8YSZ瓷体的合理烧结工艺。以La₂O₃, MnO₂和SrCO₃为原料,通过固相反应合成制备了混合导体材料La1-xSrxMnO₃（LSM）。通过分析得到LSM反应合成机理为:反应过程先是La₂O₃+SrCO₃→La2SrOx+CO₂,然后为La₂O₃+MnO₂→LaMnO₃,最后发生La2SrOx和LaMnO₃向La1-xSrxMnO₃转化,获得要求的产物。采用铂浆粘结法,制备了致密扩散障极限电流氧传感器,解决了小孔和多孔型极限电流型氧传感器长期使用时容易造成小孔堵塞,变形等问题。研制了测试系统,测试结果显示:这种传感器在0～21%的全氧浓度范围内都能得到很好的极限电流平台,而且电流与氧浓度有很好的线性关系,所制得的传感器内阻低,输出电流大,氧测量范围宽。研究了利用氧化铈的储氧特性来制备氧浓差型氧传感器,克服了传统浓差型氧传感器制作工艺复杂、成本高、不便于微型化的缺点。并利用添加锆和钇形成铈锆复合固溶体氧化物（CZO）和铈锆钇复合固溶体氧化物（CZYO）来改善其氧储能力（OSC）,采用共沉淀法制备了CZO和CZYO体系储氧材料,研究了老化温度对其相结构、比表面积及氧储能力的影响。利用事先配制好的不同空燃比的混合气体模拟尾气对制作的传感器进行测试,结果显示:输出电势不像传统氧浓差型氧传感器为1000～100mv,贫燃时,输出电势为负,富燃时,输出电势为正。设计了一种带致密扩散障的厚膜极限电流氧传感器结构,采用有限元方法对加热器进行了优化设计,并进行热传导分析和热应力分析,设计结果显示:设计的传感器响应快、热应力低以及温度分布均匀,该设计、建模方法可以应用于同类电子产品的设计。更多还原

【Abstract】 At present, due to their small size, short response time, low power consumption, easy to integrate and operating stability in the rough environment, planar zirconia automotive oxygen sensors have been the dominating products in the market. According to the manufacturing process flow of oxygen sensors, issues such as the powder preparation technology, the sintering techniques, the component manufacturing and testing technology, the characterization of materials, etc. were investigated in this PhD dissertation.Firstly, the chemical co-precipitation was employed to prepare the ultra fine powders of 8mol% Yttria-Stabilized Zirconia （8YSZ） in this study. The characteristics of the powders were analyzed by laser granulometer, TG-DTG, XRD and SEM. The mechanism and influential factors of agglomeration of ultra fine 8YSZ powder prepared by co-precipitation method have been analyzed. The effects of the process parameters including solution concentration, pH value, precipitation method and temperature, type of washing liquid, calcination temperature and surfactant on particle size of 8YSZ were investigated. The optimum process parameters were obtained.Secondly, on the basis of the spherical pore model, pore micro structure models for the intermediate and final stages of sintering have been set up while densification equations are derived for the above stages of sintering. The 8YSZ powders with different grain size and agglomeration degree were first pressed under various pressure then pressureless sintered under various sintering process. The microstructure, density and line shrinkage were measured. Combining the models with the densification equations derived in this study, the effects of the sintering temperature, the size of powder particle, green density and agglomeration degree of powder on the densification were discussed. The rule of the normal grain growth for single-phase system and the effect of the doped second phase （Al₂O₃） and pore size distribution on the grain growth were analyzed by combining the grain growth kinetics and experiment. The optimum sintering process of the ultra fine 8YSZ powders were obtained.Thirdly, the mixed electronic and oxygen ion-conduction materials, La_1-xSr_xMnO₃ （LSM） powders were prepared from La₂O₃, MnO₂, and SrCO₃ by the method of solid state reaction synthesis. The reaction steps were described as follows. First, La₂O₃+SrCO₃→La₂SrO_x+CO₂, and then, La₂O₃+MnO₂→LaMnO₃, finally we obtained La_1-xSr_xMnO₃. A type of limiting current oxygen sensor with dense diffusion barrier was fabricated with the platinum paste bonding method. It was helpful to solve these questions that the sensor was easy to be occluded, change the dimension, suffer from a drift during long term operation and relatively expensive for traditional sensor with a small diffusion hole or porous ceramic layer. The testing system for the sensor was developed. The test results showed that the sensors have good oxygen-sensitiveness in whole range of air-file ratio while there was a good linear relationship between the limiting current and oxygen concentration. Moreover, the sensor had many good performances such as low resistance, high output current, and wide measure range.Fourthly, a novel potentiometric oxygen sensor employing the oxygen storage material CeO₂ as a solid-state reference was developed. It overcame the problems of the traditional oxygen sensor such as complex fabrication process, high cost, trouble to miniaturize, etc. To improve the Oxygen Storage Capacity （OSC） of solid-state reference, the CeO₂-ZrO₂ and CeO₂-ZrO₂-Y₂O₃ compounds were prepared by chemical co-precipitation. The effects of high temperature on phase structure, BET surface area and OSC was studied. Tests on the sensor have been performed with various A/F value mixture gas at various operating temperature. The experimental result showed that the output voltage of the sensor was negative at lean-burn and was positive at rich-burn, different from the traditional oxygen sensor with 1000¹00mv.Finally, the structure of a thick-film amperometric sensor with dense diffusion barrier was designed. The structure of heater was optimized by the method of finite element analysis. Transient heat transfer analysis and thermal stress analysis were performed. The design results showed that the designed sensor had fast response, even temperature distribution and acceptable thermal stress. It was believed that the modeling techniques and computational approaches incorporated in this study were useful and can be applied for the development of similar products.更多还原